1. Field of the Invention
The present invention relates to circuits and methods for charging a battery pack.
2. Description of the Related Art
FIG. 1 illustrates a block diagram of a conventional battery charging circuit 100. The conventional battery charging circuit 100 includes an alternating current (AC) power source 102, an alternating current (AC) to direct current (DC) converter 104, a switch 106, a pulse type charger controller 112, and a battery pack 110. The AC power source 102 provides an AC voltage. The AC to DC converter 104 converts the AC voltage to a DC voltage. The DC voltage is provided to the battery pack 110 through the switch 106. The switch 106 is switched on and off by the pulse type charger controller 112, such that current pulses averaging at a desired charging current may be generated and provided to the battery pack 110. Specifically, while the switch 106 is switched on, a current is provided to the battery pack 110. While the switch is switched off, no current is provided to the battery pack 110. As such, the battery pack 110 is charged in a pulse charging mode. The battery pack 110, the switch 106, and the pulse type charger controller 112 constitute a remote control loop, which regulates a charging process of the battery pack 110 according to a status of the battery pack 110. However, the pulse type charger controller 112 utilized herein is typically complicated and expensive.
FIG. 2 shows a schematic diagram of a conventional AC to DC converter 200 which can be utilized in the conventional battery charging circuit 100 for providing a DC voltage. Elements labeled the same in FIG. 1 have similar functions and will not be repetitively described herein for purposes of brevity and clarity. The AC to DC converter 200 includes a diode bridge 202 and a capacitor 204. The diode bridge 202 converts an AC voltage from the AC power source 102 to a pulsing voltage. The capacitor 204 filters the pulsing voltage to output a DC voltage. However, when the battery pack 110 has been deeply discharged, the charging current provided by the AC to DC converter 200 may have negative effects on the battery life. Additionally, if the AC power source 102 is unstable the DC voltage will also be unstable, which can also shorten the battery life.
FIG. 3 shows a schematic diagram of another conventional AC to DC converter 300 which can be utilized in the conventional battery charging circuit 100 for providing a DC voltage. Elements labeled the same in FIGS. 1 and 2 have similar functions and will not be repetitively described herein for purposes of brevity and clarity. The AC to DC converter 300 includes the diode bridge 202, the capacitor 204 and a DC to DC converter 302. The DC to DC converter 302 includes a flyback transformer 304, a rectifying diode 306, a filtering capacitor 308, an error amplifier 310, a feedback network comprising a resistor 312, a resistor 314, an optoisolator 316, a switch mode power supply (SMPS) controller 318, and a flyback switch 320. The DC voltage produced at the capacitor 204 is converted to a DC voltage DC_IN by the flyback transformer 304, the rectifying diode 306 and the filtering capacitor 308. Furthermore, a voltage divider constituted by the resistors 312 and 314 derives a feedback voltage VFB from the DC voltage DC_IN. The feedback voltage VFB is compared with a reference voltage VREF1 at the error amplifier 310. An output of the error amplifier 310 is coupled to a primary side of the flyback transformer 304 sequentially through the optoisolator 316, the SMPS controller 318, and the flyback switch 320, thereby regulating a voltage level of the DC voltage DC_IN until the feedback voltage VFB is equal to the reference voltage VREF1. As such, the elements in the DC to DC converter 302 constitute a local control loop to regulate the DC voltage DC_IN. As such, the DC voltage DC_IN will be regulated by the local loop according to the reference voltage VREF1.
Similarly, when the battery pack 110 has been deeply discharged, the charging current provided by the AC to DC converter 300 may have negative effects on the battery life. Furthermore, the local control loop and the remote control loop (in FIG. 1) will make stability issues complicate and cause transient responses in the battery charging circuit 100.
FIG. 4 is a schematic diagram of another conventional battery charging circuit 400. Elements labeled the same in FIGS. 1, 2 and 3 have similar functions and will not be repetitively described herein for purposes of brevity and clarity. The battery charging circuit 400 includes the AC power source 102, the AC to DC converter 104, a continuous type charger controller 402, and the battery pack 110. The continuous type charger controller 402 regulates the charging process of the battery pack 110 according to a status of the battery pack 110. Furthermore, a microcontroller 404 may be employed to collect signals representing the status of the battery pack 110 and then send these signals to the continuous type charger controller 402. As such, the continuous type charger controller 402, the microcontroller 404, and the battery pack 110 constitute a remote control loop. The continuous type charger controller 402 provides a continuous charging current to the battery pack 110. In this instance, the battery pack 110 is charged in a continuous charging mode.
However, such local control loop and the remote control loop still make stability issues complicate and cause transient responses in the battery charging circuit 400. Additionally, the component count is large.